In general, a seat rotatably provided on a vehicle body includes a latching device at its leg or another part, and the seat is fastened to the vehicle body by the engagement of the latching device with a striker fixed to the vehicle body. This latching device is configured, as disclosed in Patent Literature 1 for example, such that rotating parts such as a latch and a ratchet are supported in a base plate. Generally, the base plate, the latch and the ratchet used for the latching device for vehicles are made of steel material.